Intermediate shaft gear for 901/06, 3 bolts versus 6

[Daves911L]

I have purchased a new aluminum "0" gear for the intermediate shaft. But when changing it today I realized that the early style intermediate shaft uses 3 bolts and 3 pins, instead of 6 bolts like the later shafts. Does anyone see a problem with opening up the 3 pin holes in the intermediate shaft flange and tapping them for bolts? Or is there some other solution for this?
Thanks,
Dave

[Daves911L]

Whoops! Nevermind. I just realized that the later gear is different from the early gear. The offset of the flange is different. Now I need to find a new early gear. Yeah, I'll bet those are real common!

[Eagledriver]

I think there are shops that can modify your case to fit the later shaft. That might be a better solution.

-Andy

[Daves911L]

Round 3. I'm baffled. All of the vendors I've looked at, including the host of this forum, offer only one gear for all cars '65-'89. But the gear on the early int. shaft is clearly different. Installing the new gear on the early shaft positions the the gear about 4mm closer to the oil pump. I know this can't be right. Am I just overlooking something obvious?

Andy, thanks for the suggestion. If I can avoid it though, I'd rather not modify the case. This particular motor has run beautifully its entire life (some 250K miles) and outside of the gear getting beat up by a loose chain many years ago the case internals look as good as the day they left Germany . Its going back together bone stock and all correct parts and I expect its second incarnation to outlast me.

[Walt Fricke]

If you flip the gear, will that move it in the direction you need? Or make it farther out of alignment? Can you reposition the crank gear?

I got some straight cut steel gears for this drive, but found they were cut (from dimensions I had provided from a later shaft and shop manual) for the later drives. I had not realized the early drives were different in that respect.

I was able to flip something, and it reduced the mismatch (though not 100%). This worked just fine for over 10 years of race motor (8,000 rpm) use with no problems.

Though no aluminum was involved here. Lack of full engagement might put more stress on the aluminum teeth.

I'd take the parts to a machinist to discuss what he might be able to do to move things around a bit to get a full mesh.

If the pins don't fit tightly with your newer gear, you are on the right track thinking of pulling them and tapping the holes. Works fine.

[BURN-BROS]

Dave,

The intermediate gear flange for early aluminum cases is in a different location than the rest of the 911 engines.

As a result, the gear is also different.


The Later intermediate shafts for the mag cases that have three bolts can be modded to accept 6 bolts and new gears.

Edit; Different Gear.....New gears are not available from Porsche....perhaps aftermarket...

[Daves911L]

Thanks Walt and Aaron for your replies. I have my immediate problem solved by robbing a serviceable gear from a spare shaft I had. Not my preferred solution, but quick and practical. I had already drilled and tapped my original shaft so then I had to drill the used gear for bolts instead of pins. One thing always leads to another. Walts' confirmation that this was acceptable gave me peace-of-mind.

The best resolution would probably be an approx. 2 mm spacer between the flange and gear. Before I button this case back up I will work it out exactly, and maybe try this on my spare shaft. Walt suggested flipping the gear around. This won't work on the aluminum gear, but there is a small offset to the steel gear on the crank, and flipping it may align it very close with a late gear on the early shaft. Will have to test this and see if there is clearance in the case, and between the aluminum gear and forward chain.

What I find most irritating is that all the parts vendors list the gear they sell as fitting '65-'89. NOT true. In addition to the flange offset, the new gear is also thinner than the old. Wish I'd known this earlier.